Textured-grain-powder metallurgy tantalum sputter target

ABSTRACT

The sputter target includes a tantalum body having tantalum grains formed from consolidating tantalum powder and a sputter face. The sputter face has an atom transport direction for transporting tantalum atoms away from the sputter face for coating a substrate. The tantalum grains have at least a 40 percent ( 222 ) direction orientation ratio and less than a 15 percent ( 110 ) direction orientation ratio in an atom transport direction away from the sputter face for increasing sputtering uniformity.

FIELD OF THE INVENTION

[0001] This invention relates to the field of tantalum sputter targets.In particular, this invention relates to powder metallurgy tantalumsputter targets.

BACKGROUND OF THE INVENTION

[0002] Conventional tantalum sputter targets manufactured by casting andthermomechanical processing display alternating bands of the (200) and(222) crystallographic orientations across a sputter target's face andthrough the target's cross section. For example, the target's surfaceoften exhibits alternating lighter shaded grains near the (200)orientation and darker shaded grains near the (222) orientation.Unfortunately, the (200) texture bands have a lower sputter yield thanthe (222) texture bands that result in substrates having tantalumsputter layers of varied thicknesses within a substrate. For example,sheet resistance uniformity of sputtered films for the 49 point testtypically ranges between 2 and 3 percent 1 sigma (or one standarddeviation). These non-uniform tantalum layers can cause manufacturers toincrease sputtering thickness to eliminate thin regions. Furthermore,the resulting variation in tantalum thickness often precludes the use ofsputtered tantalum films for demanding applications.

[0003] In the past, manufacturers have used grain growth techniques tocontrol grain orientation. For example, Dunn et al., in U.S. Pat. No.3,335,037, disclose a rolling/grain recrystallization method forproducing tantalum foil. This method maximizes the (110) orientation toproduce the tantalum foil—this product's thickness and grain orientationare each unacceptable for sputter target manufacturing.

[0004] Zhang, in U.S. Pat. No. 6,193,821, discloses a thermomechanicalprocess for deforming a pure tantalum billet into a sputter target. Thisprocess first relies upon side-forging or side-rolling and then uponupset forging or upset rolling. The process produces sputter targetshaving a predominantly (222) texture and a grain size of less than 25μm. This process does not appear to eliminate all banding effectsassociated with targets formed from cast tantalum targets or align the(222) texture in a direction normal to the sputter target's face.

[0005] In another thermomechanical process, Michaluk et al., in Pat.Pub. No. WO 00/31310 disclose a process for casting and processingtantalum sputter targets. This process appears to produce tantalumblanks having a primary (222) texture in a direction normal to thesputter target's face with minimal (200)-(222) texture bandingthroughout the thickness of the blanks. (This specification refers todirections with the convention that for a body-centered cubic (bcc)lattice, h+k+l must equal an even number for the reflection to have anon-zero intensity, the bcc lattice gives rise to a systematic absencewhen h+k+l is odd. For example, this specification refers to (222) and(200) directions rather than the (111) and (100) directions referencedby other conventions.) Unfortunately, controlling the (222) and (200)directions alone does not provide the necessary grain orientation orcontrol required for the most stringent sputtering applications.

SUMMARY OF THE INVENTION

[0006] The sputter target includes a tantalum body having tantalumgrains formed from consolidating tantalum powder and a sputter face. Thesputter face has an atom transport direction for transporting tantalumatoms away from the sputter face for coating a substrate. The tantalumgrains have at least a 40 percent (222) direction orientation ratio andless than a 15 percent (110) direction orientation ratio in an atomtransport direction away from the sputter face for increasing sputteringuniformity.

BRIEF DESCRIPTION OF THE DRAWING

[0007]FIG. 1 is a schematic top view of a textured-grain-powdermetallurgy tantalum sputter target.

[0008]FIG. 2 is a schematic cross section of the sputter target of FIG.1 taken along plane 2-2.

DESCRIPTION OF PREFERRED EMBODIMENT

[0009] Textured-grain-powder metallurgy tantalum targets fabricated tomaximize the (222) direction orientation ratio and minimize the (110)direction orientation ratio provide a significant improvement in sheetresistance uniformity in comparison to conventional wrought tantalumtargets. For purposes of this specification, orientation ratio isdefined as the relative proportion of a particular grain orientation inrelation to total grains, expressed in percent. For example, grainorientation may be calculated measuring the intensity of an x-ray peakand dividing it by the relative intensity of that peak listed in theJoint Committee on Powder Diffraction Standards (JCPDS) card. This ratiois then multiplied by 100 percent and normalized, i.e. divided by thesum of all grain orientation ratios between the intensities and theircorresponding relative intensities.

[0010] Referring to FIGS. 1 and 2, a typical target 10 contains atantalum body 12 and a backing plate 14. Advantageously, backing plate14 has a copper, copper alloy or aluminum alloy construction to lowerfabrication costs and improve the mechanical integrity of the target.The tantalum body 12 has a sputter face 16. The sputter face has an atomtransport direction D for transporting tantalum atoms away from thesputter face 16 for coating a substrate 20. The target uses the atomtransport direction as a reference direction for the textured grains.Most advantageously, the atom transport direction D is orthogonal to thesputter face 16.

[0011] The textured-grain-powder metallurgy tantalum targetpreferentially aligns the grains in the (222) direction with the atomtransport direction. The (222) direction is the close-packed directionfor bcc crystal structures. The target contains at least about 40percent (222) direction orientation ratio to improve sputteringuniformity. Advantageously, the target contains at least about 45percent (222) direction orientation ratio to further improve sputteringperformance. The target most advantageously contains at least about 50percent (222) direction orientation ratio to facilitate effectivesputtering. Experimental tantalum sputtering has shown that sputteringperformance increases with greater (222) direction grain alignment inthe atom transport direction. However, maximizing the (222) directionalone is insufficient to produce sputter targets with exceptionalsputtering uniformity.

[0012] In addition to maximizing the grains having the (222) direction,the sputter target must also minimize the grains having the (110)direction as aligned with the atom transport direction. For example,powder metallurgy targets having a relatively high orientation ratio of(222) direction grains and about 25 percent (110) direction orientationratio have a sputtering performance equal to traditional wrought sputtertargets. Maintaining the orientation ratio of the (110) direction belowabout 15 percent in the atom transport direction is critical toachieving excellent sputtering results. Advantageously, the sputtertarget contains an orientation ratio in the (110) direction of less thanabout 10 percent in the atom transport direction to further maximizesputtering uniformity. Most advantageously, the sputter target containsan orientation ratio in the (110) direction of less than about 5 percentin the atom transport direction to further maximize sputteringuniformity. Furthermore, careful control of tantalum powder'sconsolidation and subsequent processing can maintain orientation in the(110) direction to less than about 3 percent in the atom transportdirection.

[0013] Unlike the (222) and (110) directions, the (200), (211) and (310)directions have minimal impact upon sputtering performance.Advantageously, the target maintains each of the orientation ratios ofthe (200), (211) and (310) directions aligned with the atom transportdirection to less than about 30 percent to maintain sputteringuniformity. Most advantageously, the target maintains each of theorientation ratios of the (200), (211) and (310) directions aligned withthe atom transport direction to less than about 25 percent to maintainsputtering uniformity.

[0014] Forming the tantalum body from consolidating powder eliminatesthe visible (200)-(222) banding often associated with wrought sputtertargets. Eliminating the banding provides a further increase in sputterfilm uniformity. In addition, the sputter targets optionally have agrain aspect ratio of less than about 1.5. For purposes of thisspecification, aspect ratio is grain length measured in the thicknessdirection divided by the grain length measured in a direction parallelwith the plane of the sputter face. Most advantageously, the aspectratio is less than about 1.3.

EXAMPLE 1

[0015] The following table summarizes preliminary experiments conductedin a 603 batch sputter system manufactured by MRC with 4″ (10 cm)diameter targets. Sputter testing in this system was conducted at apower of 640 W for up to 15 kWh, a wafer scan speed of 16 cm/mincorresponding to a film thickness of 1000 Å, a chamber pressure of 10mTorr, and a target-to-wafer spacing of 2.0 inches (5.1 cm). The sheetresistance was measured at 9 points on silicon oxide wafers having adiameter of 75 mm with a 6 mm edge exclusion.

[0016] For purposes of this specification lettered targets representcomparative examples and numbered targets represent examples of theinvention. Although the sputter conditions were not optimized, allexperiments were conducted under identical conditions and thereforeallowed a comparison between a cast and thermomechanically processedreference target (Target A) and various powder metallurgy targets(Targets B to G and 1). Orientation ratios contained in the Exampleswere calculated from x-ray peak intensities as described above. TABLE 14″ (10 cm) Sputter Targets Property A B C D E F 1 Rs  2 kWh 4.8 8.3 4.64.9 7.7 4.4 4.3 Uni-  5 kWh 5.1 2.2 4.8 4.7 7.2 4.9 4.5 formi- 10 kWh6.2 N/A 4.4 5.2 7.2 5.2 4.5 ty 15 kWh 6.4 2.0 6.5 5.2 7.2 5.3 4.1 (%)Grain Size  50-100 38 26 N/A 111 32 34 (microns) Aspect Ratio 1.0-1.51.3 1.4 N/A 1.1 1.4 1.1 Orien- (110) 30 30 33 34 29 32 1 tation (200) 1919 17 17 19 18 20 Ratios (211) 15 15 16 15 16 15 10 (%) (310) 16 17 1715 17 17 9 (222) 20 19 17 19 19 18 60

[0017] Target 1, having a high orientation ratio of the (222) directionand a low orientation ratio of the (110) direction displayed optimumsputter and microstructural properties. The manufacturing parameters ofthis target were then selected for full-scale testing with 12″ (30 cm)RMX-12 targets in an Eclipse sputter system.

EXAMPLE 2

[0018] The powder metallurgy RMX-12 sputter targets exhibited an averagegrain size of 40 to 50 microns and a high (222) crystallographicorientation ratio.

[0019] Sputter testing in the Eclipse system was conducted at a power of10 kW for up to 50 kWh, a deposition time of 60 seconds, an argon flowrate of 100 sccm, a chamber pressure of 15 mTorr, a wafer temperature of150° C., and a target-to-wafer spacing of 2.5 inches (6.4 cm). The sheetresistance was measured at 49 points on silicon oxide wafers having adiameter of 150 mm with a 6 mm edge exclusion.

[0020] Table 2 summarizes grain orientation data of a conventionaltarget manufactured by casting and thermomechanical processing (TargetG) and two powder metallurgy targets with forging (Target 2) and withoutforging (Target 3). TABLE 2 Grain Orientation Ratio (Percent)Cast/Pressed P/M Target P/M Target Grain Target (Forged) (Not Forged)Orientation G 2 3 (110) 30 1 1 (200) 19 20 20 (211) 15 10 10 (310) 16 99 (222) 20 60 60 (200)-(222) Yes No No Banding

[0021] Table 2 illustrates the dramatic difference in (110) directionorientation ratio and (222) direction orientation ratio achieved withthe textured-grain-powder metallurgy targets. Furthermore, thetextured-grain-powder metallurgy targets were free of the deleterious(200)-(222) banding often associated with cast and worked products—thesetargets did not contain any (200)-(222) banding visible withoutmagnification after macro-etching in a solution of 50 volume percenthydrofluoric acid and 50 volume percent hydrogen peroxide. Furthermore,the macro-etched targets did not contain any (200)-(222) bandingdetectable by Electron Back-Scattering Diffraction (EBSD)-EBSDdetermines a target's grain orientations throughout its entirethickness.

[0022] Table 3 summarizes 1 sigma sheet resistance uniformity data forthe Targets of Table 2. TABLE 3 1 Sigma Sheet Resistance Uniformity (%)Cast/Pressed P/M Target P/M Target Target Target (Forged) (Not Forged)Life G 2 3 (kWh) Wafer 1 Wafer 2 Wafer 1 Wafer 2 Wafer 1 Wafer 2 12 2.762.78 1.32 1.47 1.15 1.07 20 2.81 2.86 1.15 1.21 1.40 1.10 50 2.97 2.911.33 1.16 1.10 1.14

[0023] The powder metallurgy sputter target 2 was manufactured byconsolidating powder to a density close to the theoretical density,rolling, annealing, solder bonding to backing plates, and machining.Adding an optional forging step before target 2's rolling step fortarget 3 showed no significant effect on the sheet resistance uniformityof the sputtered films or the appearance of the sputtered targetsurface. The textured sputter targets 2 and 3 each coated the substratewith a maximum of less than about 1.5 percent 1 sigma sheet resistanceuniformity in the rotating magnetron sputtering chamber using the RMXtype magnet.

[0024] Tantalum sputter targets manufactured by consolidating powder toa density close to the theoretical density, followed by rolling andannealing, did not display alternating texture bands and exhibited asignificantly improved sheet resistance uniformity. While examples forfabricating target blanks are given, it is noteworthy that thisinvention can be used with similar effectiveness if the target blanksare fabricated using different methods. Blank fabrication methods mayinclude but are not limited to rolling, forging, pressing, andcombinations thereof.

[0025] As illustrated in Tables 2 and 3, carefully controlling the (110)and (222) crystallographic orientations improves sputtering results. Inparticular, textured-grain-powder metallurgy sputtering targets havinglow (110) crystallographic orientation combined with high (222)orientation and the absence of alternating (222) and (200) texture bandshave improved sputter performance in comparison to conventional wroughttargets. For example, these targets have lowered sheet resistanceuniformity of sputtered films from above 2.7 percent to between 1.1 and1.5 percent (1 sigma).

[0026] Many possible embodiments may be made of this invention withoutdeparting from the scope thereof, it is understood therefore that allmatter set forth herein is to be interpreted as illustrative and not ina limiting sense.

We claim:
 1. A tantalum sputter target, the sputter target comprising: atantalum body having tantalum grains formed from consolidating tantalumpowder, the tantalum body having a sputter face, the sputter face havingan atom transport direction for transporting tantalum atoms away fromthe sputter face for coating a substrate, the tantalum grains having atleast about a 40 percent (222) direction orientation ratio and less thanabout a 15 percent (110) direction orientation ratio in an atomtransport direction away from the sputter face for increasing sputteringuniformity.
 2. The sputter target of claim 1 wherein the atom transportdirection is orthogonal to the sputter face.
 3. The sputter target ofclaim 1 wherein the grains have at least about a 45 percent (222)direction orientation ratio and less than about a 10 percent (110)direction orientation ratio in the atom transport direction.
 4. Thesputter target of claim 1 wherein the grains have less than about a 30percent (200) direction orientation ratio, less than about a 30 percent(211) direction orientation ratio and less than about a 30 percent (310)direction orientation ratio.
 5. A tantalum sputter target, the sputtertarget comprising: a tantalum body having tantalum grains formed fromconsolidating tantalum powder, the tantalum body having a sputter face,the sputter face having an atom transport direction for transportingtantalum atoms away from the sputter face for coating a substrate, thetantalum grains having at least about a 45 percent (222) directionorientation ratio, less than about a 30 percent (200) directionorientation ratio, less than about a 30 percent (211) directionorientation ratio, less than about a 30 percent (310) directionorientation ratio and less than about a 10 percent (110) directionorientation ratio in the atom transport direction away from the sputterface for increasing sputtering uniformity.
 6. The sputter target ofclaim 5 wherein the atom transport direction is orthogonal to thesputter face.
 7. The sputter target of claim 5 wherein the grains haveat least about a 50 percent (222) direction orientation ratio and lessthan about a 5 percent (110) direction orientation ratio in the atomtransport direction.
 8. The sputter target of claim 5 wherein the grainshave less than about a 25 percent (200) direction orientation ratio ,less than about a 25 percent (211) direction orientation ratio and lessthan about a 25 percent (310) direction orientation ratio.
 9. A tantalumsputter target, the sputter target comprising: a tantalum body havingtantalum grains formed from consolidating tantalum powder, the tantalumbody having a sputter face, the sputter face having an atom transportdirection for transporting tantalum atoms away from the sputter face forcoating a substrate, the tantalum grains having at least about a 50percent (222) direction orientation ratio, less than about a 25 percent(200) direction orientation ratio, less than about a 25 percent (211)direction orientation ratio, less than about a 25 percent (310)direction orientation ratio and less than about a 5 percent (110)direction orientation ratio in the atom transport direction from thesputter face for increasing sputtering uniformity and the tantalum bodybeing free of (200)-(222) direction banding detectable by ElectronBack-Scattering Diffraction.
 10. The sputter target of claim 9 whereinthe atom transport direction is orthogonal to the sputter face.
 11. Thesputter target of claim 9 wherein the target coats the substrate with amaximum of about 1.5 percent 1 sigma sheet resistance uniformity in arotating magnetron sputtering chamber using an RMX type magnet.